1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to optical amplification technology and optical oscillation technology, and in particular to an optical pumping device that is a combiner of pumping light and signal light, a multi-core fiber that is a component thereof and a manufacturing method thereof, an optical pumping device that uses the multi-core fiber, and a fiber laser and a fiber amplifier that use the optical pumping device.
2. Description of the Related Art
As a related art optical pumping device, a pump combiner that uses a multi-hole capillary has been proposed (for example, refer to Non-Patent Document 1).
Also, as a combiner of pumping light and signal light, for example, the technology disclosed in Patent Documents 1 to 7 has been proposed.    [Non-Patent Document 1] Tanaka, Tanigawa, Nakai, Sakai, Himeno, “Pump Combiner that utilizes capillary for designing flexibility” Proceedings of the IEICE General Conference, B-13-29, 2006.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H07-140346    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H06-67055    [Patent Document 3] Japanese Unexamined Patent Application, First Publication No. H06-235841    [Patent Document 4] U.S. Pat. No. 5,268,979    [Patent Document 5] U.S. Pat. No. 5,339,372    [Patent Document 6] U.S. Pat. No. 7,016,573    [Patent Document 7] U.S. Pat. No. 5,129,021
However, there are the following problems in the related art mentioned above.
The multi-hole capillary (alignment member) that is disclosed in Non-Patent Document 1 is substantially made from nearly pure silica similarly to the constituent material of the optical fibers to be inserted, and the softening temperature of the alignment member is not taken into account.
If the softening temperature of the optical fibers to be inserted and the softening temperature of the alignment member are the same, or the softening temperature of the alignment member is higher, the optical fibers become soft at nearly the same time as or earlier than the alignment member when fusion integrating by heating. This causes (A) deformation of the cross-sectional shape of the inserted fibers and (B) bending of the inserted fibers. Therefore, the following problems arise: (1) the numerical aperture (NA) of the fiber that guides the pumping light effectively increases, and the splice loss between a multi-core fiber and a bridge fiber or double-clad fiber downstream thereof increases, and (2) due to the inserted fibers becoming fusion integrated in a bent state, loss of the signal light and pumping light occurs (or increases) due to the bending. Accordingly, the multi-hole capillary made of silica that is disclosed in Non-Patent Document 1 has the above problems (1) and (2).
In all the devices that are disclosed in Patent Documents 1 to 5, the alignment member is not a multi-hole structure.
The device disclosed in Patent Document 6 involves a system of bundling optical fibers in a single-hole capillary, but an alignment member having a multi-hole structure not disclosed. Also, in Patent Document 6, there is no disclosure with respect to the softening temperature of the material.
The device disclosed in Patent Document 7 was not designed by taking the softening temperature into account. Also, it is a structure that achieves coupling by elongating the capillary itself, and is not a multi-core fiber of a type that splices with a double-clad fiber that has a rare earth-doped core via a separately elongated bridge fiber.